Optical article for illuminating building interiors employing reflective grid panel

ABSTRACT

An optical article for illuminating building interiors including a reflective grid panel, an LED light source positioned above the reflective grid panel and configured to illuminate the reflective grid panel at incidence angles ranging from a minimum angle of 0° to a maximum angle of at least 45°, a light diffusing sheet of an optically transmissive dielectric material approximately coextensive with and oriented generally parallel to the reflective grid panel, and a pair of reflective side walls flanking a space between the reflective grid panel and the light diffusing sheet. The reflective grid panel incorporates a plurality of parallel longitudinal walls and a plurality of parallel transverse walls joining the walls and defining a plurality of rectangular openings configured to transmit light. Each of the parallel transverse walls extends transversely with respect to a plane of the reflective panel and is configured to diffusely reflect a portion of the light being transmitted through the plurality of rectangular openings.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 15/687,471filed on Aug. 26, 2017, which is a continuation of application Ser. No.14/858,850 filed on Sep. 18, 2015, which is a continuation ofapplication Ser. No. 14/561,030 filed on Dec. 4, 2014, which is acontinuation of application Ser. No. 13/970,337 filed on Aug. 19, 2013,which claims priority from U.S. provisional application Ser. No.61/691,264 filed on Aug. 21, 2012, incorporated herein by reference inits entirety, and U.S. provisional application Ser. No. 61/775,678 filedon Mar. 10, 2013, incorporated herein by reference in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC

Not Applicable

NOTICE OF MATERIAL SUBJECT TO COPYRIGHT PROTECTION

A portion of the material in this patent document is subject tocopyright protection under the copyright laws of the United States andof other countries. The owner of the copyright rights has no objectionto the facsimile reproduction by anyone of the patent document or thepatent disclosure, as it appears in the United States Patent andTrademark Office publicly available file or records, but otherwisereserves all copyright rights whatsoever. The copyright owner does nothereby waive any of its rights to have this patent document maintainedin secrecy, including without limitation its rights pursuant to 37C.F.R. § 1.14.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to improving natural lighting withinbuildings and more particularly to daylight harvesting for buildinginterior illumination. More particularly, this invention relates todaylighting elements of a building such as glazed wall openings, wallwindows, roof windows and skylights, as well as to various devices andglazing structures used for admitting and distributing daylight into theinterior of a building, such as light shelves, light redirecting blindsor louvers, light diffusers, and optically transmissive plates and lightguides employing total internal reflection surfaces.

2. Description of Background Art

Various optical structures for redistributing daylight into buildinginteriors are known. At least some of such prior art devices employplanar transparent plates of glass or plastic materials which includereflective surfaces embedded between the opposing sheet surfaces andconfigured to reflect light by means of a total internal reflection(TIR). The use of TIR structures generally allows for much larger bendangles compared to refractive structures such as prismatic sheets orfilms. Large bend angles are particularly important for redistributingdaylight in the interior of a building so that at least a portion of theincident daylight could be directed towards the upper portions of theinterior, such as the ceiling of a room.

For example, one such light redirecting structure employing internal TIRsurfaces is disclosed in U.S. Pat. No. 737,979 which shows a glass plateincluding a series of parallel slots made in its body. The angle ofthese slots is such that daylight coming from any given principaldirection from outside is reflected from the surface of the slot and ishereby redirected from its original propagation path. Another lightredirecting structure is disclosed in U.S. Pat. No. 6,424,406 whichdescribes optical diffuser plates made from transparent plastics andemploying either thin strips of another plastic or hollows in therespective plates to deflect light.

U.S. Pat. No. 7,416,315 discloses a faceted reflector which includes aplurality of parallel prismatic reflectors embedded in a carrier andreflecting light by total reflection at a part of the cavity interfaces.In U.S. Pat. No. 6,616,285, total reflection surfaces are formed bymerging two optical bodies each having surface groves whichinterpenetrate into one another when such bodies are placed face-toface. U.S. Pat. No. 5,880,886 shows V-section grooves formed in a majorface of a substantially flat and planar optical element. U.S. Pat. No.4,557,565 discloses a planar solid transparent light deflecting panel orplate for transmitting sunlight into the interior of a building. Thepanel or plate is formed of a plurality of parallel identically spacedapart triangular ribs on one face. The ribs have specially selectedslopes to totally internally reflect light when such panel or plate isplaced over an opening such as window.

On the other hand, various methods of making the light redirecting TIRstructures in such transparent plates have been proposed. For example,U.S. Pat. No. 4,989,952 discloses a method for producing a transparentlight deflecting panel comprising making a series of parallel cuts in asheet of transparent solid material with a laser cutting tool. Suchpanel can be positioned in an opening in the facade of a building todeflect incident daylight towards the ceiling thereby improving thenatural lighting within the building. The transparent sheet is commonlyacrylic and the laser tool is a carbon dioxide (CO₂) laser.

U.S. Pat. No. 6,580,559 describes a method of forming internal TIRstructures in transparent panels made from glass-like thermoplasticmaterial such as PMMA by inducing parallel crazes in the thermoplasticmaterial. An organic solvent is applied on the panel surface while atensile stress is applied to a panel which results in generation ofwedge-shaped deformations (crazes) which propagate within the material.However, such method of forming internal TIR structures offers littlecontrol over the spacing, depth and extent of the crazes, as well as cansubstantially compromise the structural integrity or rigidity of thepanel.

However, the use of prior art light redirecting devices for daylightingpurposes can be deficient in that such devices only provide lightredirection in one angular dimension, whereas the significant seasonaland hourly positional changes of the sun are two-dimensional (i.e.,changes in the elevation and azimuth angle). Thus, many daylightingsystems would benefit from employing a sheet-form light redirectingstructure that can provide large bend angles in more than one angulardimensions and thus provide a more uniform and broad distribution ofdaylight in the building interior. On the other hand, such daylightingsystems will also benefit from providing additional means for lightdiffusion which would even further improve light distribution and reduceapparent glare.

These needs and others are met within the present invention, whichprovides an improved sheet-form structure for illuminating buildinginteriors with sunlight and also provides a method of making the same.The improved sheet-form structure employs internal reflective surfacesdisposed in an arrangement which is more efficient for redirecting anddistributing sunlight incident from a broad range of directions.

BRIEF SUMMARY OF THE INVENTION

The present invention solves a number of daylight harvesting anddistribution problems within a planar and compact sheet-form opticalsystem which can be used in window glazing and skylights.

In one embodiment, an optical article is described for directing anddistributing daylight within building interior using an opticallytransmissive sheet material in which light redirecting functionality isprovided by two intersecting arrays of parallel channels formed in oneor both major surfaces of the sheet. Each channel has a high aspectratio (the ratio between the depth and width of the channel) andincludes two opposing side walls having generally smooth surfacesconfigured for reflecting light by means of a Total Internal Reflection(TIR). The propagation of an off-axis light beam through such sheetresults in splitting the incident beam onto two or more light beamswhich propagate towards different directions. Due to employing internalreflection, the angular spread of the emerging beam can be quite broad,depending on the incidence angle. Each of the intersecting arrays ofparallel TIR channels redirect light in the respective reflective planesso that the incident beam can be redirected and split in both angulardimensions. Thus, when such light redirecting optical article isincorporated into a skylight or fenestration system, the direct beam ofsunlight can pass through the sheet-form material configured withinternal TIR surfaces and at least a portion of the solar beam can beredirected into building interior at high deflection angles with respectto the incident direction. At least one broad-area surface of theoptically transmissive sheet may be provided with light-diffusingsurface relief features. Alternatively, or in addition to that, abroad-area light diffusing element may be provided and optically coupledto a major surface of the sheet.

In at least one implementation, the thickness of the opticallytransmissive sheet is between 1.5 mm and 30 mm. In at least oneimplementation, such sheet has a rectangular shape and is made fromPoly(methyl methacrylate).

There are various ways in which the intersecting arrays of TIR-enabledchannels may be formed and positioned with respect to each other. In oneimplementation, one array of parallel channels may be formed in onebroad-area surface of the sheet and the other array may be formed in thesame surface. In an alternative implementation, one array of parallelchannels may be formed in one broad-area surface of the sheet and theother array may be formed in the opposite surface. In at least oneimplementation, the longitudinal axis of the two arrays may be crossedat a right angle.

The geometry of light-redirecting channels may be configured in a numberof ways. In at least one implementation, at least one side wall of eachchannel is planar. In at least one implementation, at least one of suchside walls has a curvilinear cross-sectional profile. In at least oneimplementation, at least one of the side walls of each channel extendsgenerally perpendicular to the prevailing plane of the opticallytransmissive sheet. In at least one implementation, at least one of theside walls of each channel makes a dihedral angle with one of thesurfaces of the sheet which is greater than 80 degrees and less than 90degrees. In various implementations, the dihedral angle may be constantor can be made variable across the sheet surface. In at least oneimplementation, each of the channels has a generally V-shapedtransversal profile. In at least one implementation, each of thechannels has a generally deep-drawn U-shaped transversal profile.

In at least one implementation, at least one of the surfaces of theoptically transmissive sheet is provided with light-diffusing surfacerelief features and such features are selected from the group of opticalelements consisting of microlenses, microprisms, and matte surfacetexture.

In at least one implementation, the TIR channels are formed in theoptically transmissive sheet by laser cutting.

In one embodiment, the optical article is described for directing anddistributing daylight within building interior using a specularlyreflective grid and a light diffusing sheet disposed in energy exchangerelationship with the reflective grid. The reflective grid includes arectangular grid of mirrored walls. Each mirrored wall longitudinallyextends parallel to the prevailing plane of the panel and transversallyextends perpendicularly or nearly perpendicularly to such plane. Thegrid of intersecting mirrored walls creates an array of light channelingcells which redirect at least a portion of off-axis rays thus splittingan incident parallel beam into two or more beams distributed over abroad angular range. The light diffusing sheet is configured to providea further spread to the direct beam. In at least one implementation, thelight diffusing sheet is disposed on the light path before thereflective grid. In at least one implementation, the light diffusingsheet is disposed on the light path after the reflective grid. In atleast one implementation, the reflective grid is sandwiched betweenopposing parallel diffusing sheets.

In one embodiment, the optical article is described to be incorporatedinto a skylight. The optical article is configured to receive lightcollected by the skylight and redistribute such light within buildinginterior so as to provide a broader singular spread at least foroff-axis solar rays.

In one embodiment, a method of manufacturing a light redirecting opticalarticle comprising a sheet of optically transmissive rigid material isdescribed. The method includes the steps of laser-cutting a first arrayof parallel channels along a first direction using a CO2 laser andlaser-cutting a second array of parallel channels along a seconddirection, where the first and second directions are perpendicular toeach other.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

The invention will be more fully understood by reference to thefollowing drawings which are for illustrative purposes only:

FIG. 1 is a schematic perspective view of an optical article forilluminating building interiors with sunlight, according to at least oneembodiment of the present invention.

FIG. 2 is a schematic view of an optical article for illuminatingbuilding interiors with sunlight, showing an exemplary grid arrangementof channels in a surface, according to at least one embodiment of thepresent invention.

FIG. 3 is a schematic perspective view of an optical article, showing agrid of intersecting channels each having a deep-drawn V-groove shape,according to at least one embodiment of the present invention.

FIG. 4 is a schematic perspective view of an optical article, showing agrid of intersecting channels each having a narrow funnel-shapedcross-sectional profile with curvilinear walls, according to at leastone embodiment of the present invention.

FIG. 5 is a schematic cross-sectional view and raytracing of a lightredirecting optical article, showing TIR reflective walls which areperpendicular to the major surfaces of an optically transmissive layer,according to at least one embodiment of the present invention.

FIG. 6 is a schematic cross-sectional view and raytracing of a lightredirecting optical article, showing an alternative profile of channelsin an optically transmissive layer, according to at least one embodimentof the present invention.

FIG. 7 is a schematic cross-sectional view and raytracing of a lightredirecting optical article, showing a further alternative profile ofchannels in an optically transmissive layer, according to at least oneembodiment of the present invention.

FIG. 8 is a schematic cross-sectional view and raytracing of a portionof a light redirecting optical article, further showing various raypaths through a light-channeling cell, according to at least oneembodiment of the present invention.

FIG. 9 is a schematic perspective view and raytracing of a portion of alight redirecting optical article, showing an exemplary path of a rayreflecting from multiple walls of a light-channeling cell, according toat least one embodiment of the present invention.

FIG. 10 is a schematic view of an optical article for illuminatingbuilding interiors with sunlight, showing surface microstructures in abroad-area surface of an optically transmissive sheetform material,according to at least one embodiment of the present invention.

FIG. 11 is a schematic cross-sectional view and raytracing of a portionof a light redirecting optical article, illustrating the operation ofTIR surfaces and light-diffusing surface relief features, according toat least one embodiment of the present invention.

FIG. 12 is a schematic cross-sectional view of a light redirectingoptical article comprising additional layers of an opticallytransmissive material, according to at least one embodiment of thepresent invention.

FIG. 13 is a schematic cross-sectional view of a portion of a lightredirecting optical article, showing a straight channel having wallsextending perpendicular to opposing broad-area surfaces, according to atleast one embodiment of the present invention.

FIG. 14 is a schematic cross-sectional view of a portion of a lightredirecting optical article, showing a partial sloped channel, accordingto at least one embodiment of the present invention.

FIG. 15 is a schematic cross-sectional view of a portion of a lightredirecting optical article, showing an alternative sloped channel,according to at least one embodiment of the present invention.

FIG. 16 is a schematic cross-sectional view of a portion of a lightredirecting optical article, showing a channel having non-parallelwalls, according to at least one embodiment of the present invention.

FIG. 17 is a schematic cross-sectional view of a portion of a lightredirecting optical article, showing a channel having convex walls,according to at least one embodiment of the present invention.

FIG. 18 is a schematic cross-sectional view of a portion of a lightredirecting optical article, showing a channel having concave walls,according to at least one embodiment of the present invention.

FIG. 19 is a schematic cross-sectional view of a portion of a lightredirecting optical article, showing a through-cut channel, according toat least one embodiment of the present invention.

FIG. 20 is a schematic cross-sectional view of a portion of a lightredirecting optical article, showing a partial straight channel formedin a textured surface, according to at least one embodiment of thepresent invention.

FIG. 21 is a schematic cross-sectional view of a portion of a lightredirecting optical article, showing a curvilinear V-shaped channelformed in a light emitting surface, according to at least one embodimentof the present invention.

FIG. 22 is a schematic cross-sectional view and raytracing of a portionof a light redirecting optical article, showing a curvilinear V-shapedchannel formed in a light receiving surface, according to at least oneembodiment of the present invention.

FIG. 23 is a schematic cross-sectional view and raytracing of a portionof a light redirecting optical article, showing a corrugated reflectivesurface of a channel, according to at least one embodiment of thepresent invention.

FIG. 24 is a schematic cross-sectional view and raytracing of a lightredirecting optical article, further showing a light diffusing layerdisposed in optical communication with a surface of an opticallytransmissive layer, according to at least one embodiment of the presentinvention.

FIG. 25 is a schematic cross-sectional view and raytracing of a lightredirecting optical article, further showing a light diffusing layerdisposed in optical communication with another surface of an opticallytransmissive layer, according to at least one embodiment of the presentinvention.

FIG. 26 is a schematic cross-sectional view and raytracing of a lightredirecting optical article, further showing two light diffusing layersdisposed on both sides of an optically transmissive layer, according toat least one embodiment of the present invention.

FIG. 27 is a schematic cross-sectional view of a light redirectingoptical article, showing light-diffusing surface relief features formedin a major surface of an optically transmissive layer, according to atleast one embodiment of the present invention.

FIG. 28 is a schematic cross-sectional view of a light redirectingoptical article, showing light-diffusing surface relief features formedin a different major surface of an optically transmissive layer,according to at least one embodiment of the present invention.

FIG. 29 is a schematic cross-sectional view of a light redirectingoptical article, showing a light diffusing surface relief featuresformed in opposing major surfaces of an optically transmissive layer,according to at least one embodiment of the present invention.

FIG. 30 is a photograph of an exemplary implementation of a lightredirecting optical article, showing a layer of optically transmissivematerial in which a perpendicular grid of channels is cut using a CO₂laser, according to at least one embodiment of the present invention.

FIG. 31 is a schematic perspective view of a light redirecting opticalarticle, showing a specularly reflective grid panel coupled to anoptically transmissive, light diffusing element, according to at leastone embodiment of the present invention.

FIG. 32 is a schematic cross-sectional view of a portion of a lightredirecting optical article, showing an array of planar mirroredreflectors disposed perpendicularly to a prevailing plane of areflective grid panel, according to at least one embodiment of thepresent invention.

FIG. 33 is a schematic cross-sectional view of a portion of a lightredirecting optical article, showing an alternative shape of reflectors,according to at least one embodiment of the present invention.

FIG. 34 is a schematic cross-sectional view of a portion of a lightredirecting optical article, showing an alternative disposition of anoptically transmissive light diffuser with respect to a reflective gridpanel, according to at least one embodiment of the present invention.

FIG. 35 is a schematic cross-sectional view of a portion of a lightredirecting optical article, showing a reflective grid panel sandwichedbetween two light diffusers, according to at least one embodiment of thepresent invention.

FIG. 36 is a schematic cross-sectional view of an exemplary skylightimplementation of a light redirecting optical article including a layerof transparent material disposed below a dome-shaped diffuser and havingchannels formed between its major surfaces, according to at least oneembodiment of the present invention.

FIG. 37 is a schematic cross-sectional view of another exemplaryskylight implementation of a light redirecting optical article includinga specularly reflective grid panel disposed below a dome-shapeddiffuser, according to at least one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring more specifically to the drawings, for illustrative purposesthe present invention is embodied in the apparatus and method generallyshown in the preceding figures. It will be appreciated that theapparatus and method may vary as to configuration and as to details ofthe parts without departing from the basic concepts as disclosed herein.Furthermore, elements represented in one embodiment as taught herein areapplicable without limitation to other embodiments taught herein, and incombination with those embodiments and what is known in the art.

The present invention particularly seeks to provide illuminationcomponents capable of receiving daylight entering building interiorsthrough various openings, such as wall windows, roof windows, doors andskylights and redistributing such daylight for improved daylightingefficiency, more uniform spatial distribution and reduced glare.Daylight is generally referred to both the direct and indirect sunlightstriking the respective openings in buildings during the daytime. Thedirect sunlight represents a quasi-parallel beam from the sun and theindirect sunlight represents the diffuse solar radiation scattered outof the direct beam by the sky and various outdoor objects. While theoperation of the following embodiments is primarily described by exampleof the direct sunlight, it should be understood that this invention mayalso be applied for admitting and redistributing the diffuse componentof sunlight within a building interior.

A first embodiment of the present invention is directed to a sheet-formof optically transmissive, solid dielectric material which includes aplurality of TIR reflectors formed between its opposing broad-areasurfaces and arranged in a grid pattern. Suitable sheet-formrepresentations of the body of the material may include a panel, slab orfilm in which the material thickness is substantially less than theother two dimensions. While the preferred embodiments are described uponthe case of a rectangular sheet-form, it should be understood that thisinvention is also applicable to any two-dimensional shape variations ofthe sheetforms, including but not limited to a rectangle, a polygon, acircle, a strip, a freeform, or any combination therein. This inventionis further applicable to any three-dimensional shapes that can beobtained by bending the sheetforms accordingly, including but notlimited to cylindrical or semi-cylindrical shapes, conical shapes,corrugated shapes, and the like.

FIG. 1 illustrates such an embodiment of an optical article exemplifiedby a rectangular planar sheet 2 of optically clear polymeric material.Sheet 2 is defined by opposing major surfaces 10 and 20. Such surfaces10 and 20 extend parallel to each other so that sheet 2 has a generallyconstant thickness. It is preferred that the thickness of sheet 2 isconsiderably smaller than the length and width of the sheet.Particularly, it may be preferred that the thickness of sheet 2 isbetween 1.5 mm and 30 mm while the length and width of sheet 2 mayextend from several centimeters to several meters.

Sheet 2 includes a plurality of channels 4 formed in broad-area surface10. Each channel 4 forms at least two side walls extending transverselybetween surfaces 10 and 20 of sheet 2.

Each channel 4 should be sufficiently narrow so that the spacing betweenthe adjacent channels is considerably greater than the width of thechannel. At the same time, each channel 4 should preferably have arelatively high aspect ratio. The aspect ratio may be defined as theratio between the depth of the channel 4 and width of the channel at itsbase in surface 10. The aspect ratio of channels 4 is preferred to begreater than five and, more preferably, at least ten or more. Similarly,the spacing between adjacent channels 4 is preferred to be greater thanthe width of each channel by at least five times or more.

Channels 4 are arranged in two arrays which are crossed at an angle withrespect to one another so that a grid of channels 4 is formed in surface10. In a first parallel array, channels 4 longitudinally extend parallelto a reference line 370 which is hereinafter referred to as alongitudinal axis of the first array. In a second parallel array,channels 4 extend parallel to a reference line 380 which is hereinafterreferred to as a longitudinal axis of the second array. In a preferredembodiment illustrated in FIG. 1 , longitudinal axis 370 of the firstparallel array is perpendicular to longitudinal axis 380 of the secondparallel array so that the grid of channels 4 is rectangular (see alsoFIG. 2 ).

Channels 4 should be formed so that their walls extend into the materialof sheet 2 perpendicularly or near-perpendicularly to surfaces 10 and20. The surfaces of such walls should preferably be made smooth andcapable of internally reflecting light by a Total Internal Reflection(TIR). Accordingly, the grid of intersecting arrays of channels 4 mayform a plurality of light-channeling cells 30. Each light-channelingcell 30 will have a shape of rectangular parallelepiped defined by fourvertical (with respect to a horizontally disposed sheet 2) walls ofintersecting channels 4 and a horizontal terminal wall represented by anuncut portion of surface 10.

It will be appreciated by these skilled in the art that forming narrow,high-aspect-ratio channels with vertical walls may be difficult withmost industrial processes. Therefore, the preferred embodiments of thepresent invention also include the cases where the walls of channels 4extend transversally through sheet 2 at angles which are not exactlyperpendicular to surface 10 but fairly close to being perpendicular.

Such cases are illustrated in FIG. 3 and FIG. 4 where the walls ofchannels 4 form a relatively low angle (within a predetermined maximumangular value) with respect to a normal to surface 10.

FIG. 3 shows an implementation of sheet 2 where channels 4 have slopedwalls and form narrow V-grooves in surface 10. Accordingly, eachlight-channeling cell 30 of FIG. 3 will be shaped in the form of asquare frustum (truncated pyramid with a rectangular base) withnear-parallel side walls.

In FIG. 4 , the walls formed by each channel 4 are curvilinear in across-section perpendicular to the longitudinal axis of the channel.Accordingly, each light-channeling cell 30 of FIG. 4 has slightly curvedside walls which will still be nearly perpendicular to surface 10.

According to a preferred embodiment, sheet 2 can be made fromPoly(methyl methacrylate) which is also generally referred to as PMMA,acrylic or acrylic glass. However, it should be understood that anyother optically-clear plastic material having the sufficient thicknessto support the formation of channels 4 may also be used for making sheet2.

A suitable method of forming narrow, high-aspect-ratio channels 4channels 4 in surface 10 may include laser ablation using a CO₂ laseroperating at 10.6 μm. CO₂ lasers are well known in the art to be able toproduce deep micro-channels with fairly smooth, heat-polished edges inPMMA materials. Other methods may also include molding, embossing andvarious forms of microreplication in which case a suitable mold may beprovided with an array of high-aspect-ratio protrusions representing anegative replica of the channels 4 to be formed.

FIG. 5 illustrates further details and operation of the optical articleshown in FIG. 1 and depicts a cross-section of sheet 2 along referenceline 370. In such cross-section, each channel 4 of FIG. 5 has adeep-drawn U-shape and includes a first planar wall 8 and an opposingsecond planar wall 26. Walls 8 and 26 pairwise define individuallight-channeling cells 30.

The generally planar configuration of sheet 2 may be characterized by aprevailing plane of the sheet and a normal 44 to such plane. Obviously,due to the parallelism of surfaces 10 and 12 normal 44 is also a normalto both of these surfaces. Accordingly, each of the walls of channels 4has a linear cross-sectional profile extending between surface 10 and 20along normal 44. Each light-channeling cell 30 thus has a rectangularcross-section protruding away from the body of sheet 2. The depth ofeach channel 4 should preferably be substantially greater than its widthso that cells 30 are disposed sufficiently close to each other. In otherwords, the air gaps between the individual cells should preferably besubstantially smaller than the size of each cell 30.

Each of the side walls 8 and 26 of channels 4 should be configured forlight redirection by means of the Total Internal Reflection (TIR). Itwill be appreciated by those skilled in the art that TIR would normallyoccur at a smooth optical interface between a first light transmittingmaterial having a greater refractive index and a second lighttransmitting material having a lower refractive index when the angle ofincidence is greater than the critical TIR angle characterizing suchinterface. Accordingly, in order to provide TIR reflectivity, thesurface of walls 8 and 26 should be generally smooth with glossy,polished appearance.

In operation, an off-axis ray 212 striking the light receiving apertureof cell 30 at surface 10 bends into the bulk material of sheet 2 bymeans of refraction, passes through the body of the sheet and emergesfrom the opposite surface 20, also undergoing refraction. It will beappreciated by those skilled in the art that, when surface 10 and 20 areparallel and when ray 212 encounters no obstacles on its light pathwithin the transmissive layer of sheet 2, it will emerge from surface 20at essentially the same exit angle as the angle of incidence.

For the purpose of explaining the best modes of operation of the presentinvention, the term “off-axis” is generally directed to mean lightincidence onto a surface at angles other than normal to the surface.From the practical considerations, when a ray or a parallel beam oflight makes an angle with respect to the surface close to 90° but is notexactly normal to the surface, such incidence may still be consideredon-axis. In contrast, in order to be considered off-axis, the ray ore abeam should deviate notably from the normal to the surface in order tobe considered off-axis. Since the incidence angle is customarilymeasured off a normal to the surface, the on-axis rays will generallyhave zero or near-zero incidence angle and the off-axis rays willgenerally have non-zero angles in the −90° to 90° range in a plane ofincidence.

Another off-axis ray 214 initially propagating parallel to ray 212strikes the entrance aperture of the same cell 30 but at a differentlocation along the surface. Wall 8 of one of channels 4 lies on theoptical path of ray 214 which causes redirection of ray 214 by means ofTIR from wall 8. Since wall 8 is perpendicular to surface 10 and theangle of reflection is equal to the angle of incidence as a matter ofoptics, the propagation direction of ray 214 after TIR will mirror thatof ray 212 relatively to normal 44. Thus, ray 214 will emerge fromsurface 20 at the same angle with respect to normal 44 except that theexit angle will have an opposite sign compared to ray 212. Therefore,the optical article of FIG. 5 will effectively redistribute an off-axisparallel beam of incident light into at least two beams whichpropagation directions include opposing quadrants or hemispheres withrespect to normal 44 in the plane of reflection of such off-axis beam.

The use of TIR to redirect at least a portion of light toward theopposing edge of sheet 2 promotes a broader angular distribution oflight compared to refraction-only diffusers and can help illuminateportions of the building interiors more efficiently than would otherwisebe possible with prior-art designs. It will be appreciated that, sinceTIR is practically lossless, sheet 2 can be designed so that its lighttransmission remains relatively high and comparable to the transmissionof a raw polished sheet of the same material.

Without departing from the operation principle described by example ofrays 212 and 214, sheet 2 may also be operated in a reverseconfiguration in which light is received by the opposing surface 20 ofsheet 2 and exits from surface 10. This is illustrated by example ofrays 216 and 218 in FIG. 5 . Ray 216 enters sheet 2 through surface 20and emerges from opposing surface 10 undergoing refraction at eachoptical interface it encounters. Since ray 216 does not encounter anyTIR interfaces, it maintains the initial propagation direction afterpassing through sheet 2. In contrast, parallel ray 218 impinging ontosurface 20 at a slightly different location enters the light receivingaperture of cell 30 and strikes TIR wall 8 of channel 4. Similarly toray 214, ray 218 is reflected from wall 8 by means of TIR and emergesfrom surface 10 into an opposing hemisphere with respect to surfacenormal 44 compared to the case where ray 218 would have propagated inthe absence of wall 8. Accordingly, rays 216 and 218 incident into sheet2 from a single quadrant or hemisphere with respect to the surfacenormal (in the plane of reflection), are redirected into opposingquadrants or hemispheres with respect to the same normal.

FIG. 6 illustrates the operation principle of sheet 2 of FIG. 3 in whichchannels 4 are formed by V-shaped grooves in surface 10. Accordingly,the pairs of parallel rays 212, 214 and 216, 218 are redistributedwithin sheet 2 so that the respective rays emerge towards divergingdirections and towards the opposing sides of sheet 2 with respect tosurface normal 44. It will be understood that, since walls 8 of channels4 are sloped with respect to normal 44, the angles that rays 214 and 218make with normal 44 upon reflecting from wall 8 will generally not bethe same as those before the reflection. Nevertheless, when the slope ofwalls 8 and 26 is sufficiently small, as in an exemplary case of deepdrawn, narrow channels in the surface of sheet 2, the angle differencein light propagation between FIG. 5 and FIG. 6 will also be relativelysmall.

FIG. 7 illustrates a yet further example of sheet 2 operation wherechannels 4 have cuspated transversal profiles with curvilinear walls 8and 26, similarly to the case illustrated in FIG. 4 . Such cuspatedprofiles of channels 4 may be formed naturally, for example, in theprocess of direct laser ablation. Similarly to the above-describedexamples, as illustrated by the light paths of rays 212, 214 and 216,218 in FIG. 7 , a beam of parallel light can be redistributed across alarge angular range due to redirecting at least a portion of theincident beam using TIR reflectors between surfaces 10 and 20.Curvilinear walls of channels 4 may also be advantageously selected forthe purpose of additional diffusion of light passing through sheet 2.

It is noted that the light redirecting operation of sheet 2 is notlimited to light reflection from just one wall of the respective cells30. Particularly, the aspect ratio of cells 30 can be made sufficientlyhigh to enable multiple bounces of light rays from opposing walls thusproviding a light-channeling or light-guiding function. This isillustrated in FIG. 8 in which an exemplary off-axis ray 690 is shownreflecting from the TIR walls of cell 30 three times while another ray692 undergoes only a single reflection. At least some other rays (suchas a ray 694 shown in FIG. 8 ), especially those having relatively lowoff-axis deviations, may also pass through cell 30 without interactingwith any of the TIR walls. In the illustrated example, each cell 30 mayoperate as a kaleidoscopic light pipe for at least off-axis rays. Itwill be appreciated that, when cell 30 is exposed to a beam of lightwhich can be represented by a large number of off-axis rays, such rayswill randomly mix within cell 30 and emerge from surface 20 with randomangular and spatial distribution. Some rays may exit towards one edge ofsheet 2 and other rays may exit towards the opposing edge. Thus, sheet 2employing such high-aspect-ratio cells 30 may be used for improveddiffusion and distribution of daylight incident from different anglesonto the optical article in response to the diurnal and/or seasonalmotion of the sun.

It is further noted that the light-channeling operation of individualcells 30 is not limited to reflecting light from the opposing parallelTIR walls in one plane. FIG. 9 illustrates an exemplary ray path throughcell 30 where such ray enters surface 10 from a random off-axisdirection. In the illustrated case, the incident ray makes non-zeroangles with each of the side walls of the respective light-channelingcell 30. As it can be seen, the off-axis ray can be sequentiallyreflected from two or more of the four side walls of light-channelingcell 30 thus obtaining a random emergence angle from surface 20.Accordingly, the light-redirecting optical article of this invention maybe configured to provide two-dimensional randomization of the lightpaths and thus provide an improved light beam spread and homogenizationfor a broad range of incidence angles.

Sheet 2 may be provided with additional means for light diffusion and/orbeam dispersion. FIG. 10 shows sheet 2 in which surface 20 haslight-diffusing microstructure exemplified by random surface relieffeatures 6. The light-diffusing microstructure may have any2-dimensional or 3-dimensional geometry configured for dispersing orscattering a parallel beam of light by means of refracting its raystowards different directions. Any useful type of surface microstructuremay be used. Representative refractive microstructures may include butare not limited to prism arrays, arrays of prisms, lens arrays,engineered surfaces or various surface relief types commonly referred toas “frosted-glass”, “prismatic”, “sanded”, “pebble”, “ice”, “matte”,“microprism”, “microlens”, and the like. Alternatively or in addition tothat, surface 20 may have any decorative or ornamental microstructuredfeatures such as, for example, those found in some decorative or privacypanels and films.

Any conventional means used to pattern the surface of thermoplasticsheets or films may be used to form the textured surface 20. These mayinclude but are not limited to engraving, microreplication from a mastermold, etching, embossing, stamping, laser patterning, sanding, etching,and the like. The required texture may also be ordinarily obtained byreplication in a UV-curable material on a suitable opticallytransmissive substrate.

FIG. 11 illustrates the operation of the system depicted in FIG. 10 .

Referring to FIG. 11 , a quasi-parallel ray bundle 202 illustrativelyrepresents a direct beam of sunlight striking the outer surface 10 ofsheet 2 from an off-axis direction. Ray bundle 202 is reflected by sidewall 8 of one of the channels 4 by means of TIR and exits from themicrostructured surface 20 of sheet 2. Surface relief features 6 ensurethat light rays in ray bundle 202 make random incidence angles with thelight output surface 20 and are thus dispersed over a certain angularrange. The angle of dispersion may be controlled by the shape anddistribution pattern of surface relief features 6. Other ray bundles 204and 206 which exemplify direct sunlight at different solar elevationsare similarly redirected by reflection from the respective side walls 8of channels 4 and exit from the textured light-output surface 20.

While the prevailing emergence angle of ray bundles 202, 204 and 206from sheet 2 may differ from each other due to the difference in theincidence angle onto the light input surface 10, the redirected solarradiation will generally be redistributed over a relatively broadangular range in either case due to the light diffusing function ofsurface 20. It will be appreciated that such light diffusion may enhancethe daylighting experience for the building occupants by improvingdaylight distribution and reducing the glare associated with directsunlight.

Sheet 2 may comprise any number of additional internal or externallayers that can have various functions. Particularly, a layer ofoptically transmissive material may be provided on one or both sides ofsheet 2. This is illustrated in FIG. 12 showing a transparent layer 40attached to surface 10. By way of example and not limitation, layer 40may be used to provide protective encapsulation of channels 4. Suchencapsulation can help prevent dust, dirt and/or moisture accumulationin channels 4. Layer 40 may be attached to surface 10 using a pressuresensitive adhesive, a heat-activated adhesive,moisture-activated-adhesive, UV- or hear-curable adhesive, static cling,or by any other suitable means. In a further example, layer 40 itselfmay be formed by an optically clear adhesive. This may be useful, forinstance for the case when sheet 2 is intended to be laminated onto anexternal substrate.

As further illustrated in FIG. 12 , a layer 42 of optically transmissivematerial may be applied to the opposing surface 20. When a texturedsurface is desired for the optical article, surface relief features 6may be formed in such external layer 42. In an illustrative example,layer 42 may be initially formed separately from sheet 2 and thenlaminated to surface 20 of the sheet using a pressure sensitive orhot-melt adhesive. Any such external layers applied to sheet 2 may alsobe provided with UV- or IR-blocking properties. Alternatively, or inaddition to that, any of the layers may be provided with color filteringproperties or tint.

Sheet 2 may incorporate any masking elements, for example, to blockportions of light from propagating into the building interior.Furthermore, sheet 2 may incorporate any number of auxiliary layersserving various additional purposes, such as, for example, providingadditional mechanical strength, environmental resistance, peelresistance, improved visual appearance, decorative appearance, etc. Anyoptical interface between optically transmissive layers may also includean intermediate optically transmissive layer, for example, for promotingthe optical contact or adhesion between the layers.

The optical article of the present invention may further incorporatevarious color filters, inks, dyes or other devices or substances thatchange the color of the light upon passage through sheet 2. Sheet 2 mayalso incorporate light filtering or light rejecting elements, polarizingelements, fluorescent elements, light scattering or diffusing elementsand the like, which may be provided as separate layers or incorporatedinto the bulk material of the sheet.

FIG. 13 through FIG. 21 illustrate various cross-sectionalconfigurations of channels 4 in sheet 2. In FIG. 13 , channel 4 has astraight configuration with parallel side walls 8 and 26 which areextending perpendicular to surfaces 10 and 20. FIG. 14 shows channel 4formed in surface 10 of sheet 2 where walls 8 and 26 of the channel areparallel to each other but both inclined at an angle with respect to anormal to surfaces 10 and 20. FIG. 15 shows channel 4 in which the slopeangle of walls 8 and 26 with respect to the same normal mirrors that ofFIG. 14 . FIG. 16 shows channel 4 in which wall 8 extends parallel to anormal to surface 10 but wall 26 extends at an angle with respect to thesame normal. FIG. 17 shows channel 4 in a funnel-shaped configurationwith convex walls 8 and 26. FIG. 18 shows channel 4 with concavecurvilinear profiles of side walls 8 and 26.

It is noted that this invention is not limited to forming channels 4 insurface 10. At least in some embodiments, channels 4 may be formed ineither one or both of surfaces 10 and 20.

FIG. 19 illustrates channel 4 extending all the way between surface 10and 20. Its side walls 8 and 26 are parallel to each other andperpendicular to the prevailing plane of sheet 2. FIG. 20 shows partialstraight channel 4 formed in surface 20 of sheet 2 and having parallelwalls 8 and 26. In FIG. 21 , a curvilinear-profile, funnel-shapedchannel is shown formed in surface 20.

It is further noted that channels 4 forming the first parallel array insheet 2 may have different profiles than channels 4 forming the secondparallel array in said sheet. Additionally, the intersecting arrays ofchannels 4 may be formed in the opposing surfaces of sheet 2. Forexample, referring to FIG. 2 , channels 4 extending parallel to axis 370may be formed in surface 10 and channels 4 extending along axis 380 maybe formed in surface 20. The reference lines defining the orientation ofeach array may extend perpendicular to each other or make any non-zeroangle between one another. When formed in the opposing surfaces,channels 4 that are perpendicular to each other can be made intersectingand extending half-way or more through the thickness of the material ofsheet 2. Alternatively, channels 4 that are perpendicular to each othermay be staggered and extending less than half-way through the thicknessof sheet 2.

According to a preferred embodiment of the present invention, it isgenerally desired that the surfaces of side walls 8 and 26 of eachchannel 4 are made as smooth as possible in order to provide a good TIRreflectivity and minimum light scattering. However, in someapplications, some residual roughness of the TIR surfaces may be presentdue to the imperfections of the fabrication process. In certaininstances, a slight waviness of the TIR surfaces may be provided for thepurpose of controlled dispersion or diffusion of the reflected lightbeam over a limited angular range.

FIG. 22 illustrates the operation of funnel-shaped channel 4. Suchchannel 4 may be created, for example by laser ablation or by slittingsurface 10 with the subsequent stretching of sheet 2 perpendicularly tothe longitudinal axis of channel 4. Parallel rays 62 and 64, which mayexemplify the direct beam of sunlight incident onto surface 10 from anoff-axis direction, are reflected by the TIR surface of wall 8 and exitfrom the opposite surface of sheet 2. Since the surface of wall 8 iscurved, the redirected rays 62 and 64 will no longer be parallel to eachother after TIR. Accordingly, a parallel beam of light passing throughsheet 2 at the appropriate angles will be dispersed across a broaderangular range thus resulting in a more diffuse illumination of theinterior compared to the case of a planar wall 8.

FIG. 23 illustrates an alternative configuration of channel 4 wherelight diffusing properties are obtained using a different approach. TheTIR surface of wall 8 is provided with shallow corrugations whichredirect and disperse the incident beam at different angles within apredefined range of angles. Such corrugations may be formed, forexample, by laser cutting using multiple passes, by slitting with ablade having a variable thickness, by slitting using a reciprocationblade motion or by any other suitable means. Particularly, it ispreferred that the maximum slope of each corrugation is less than acritical angle at which a TIR can occur at the exit surface 20.Accordingly, parallel rays 62 and 64 striking surface 8 at differentlocations are redirected at different angles and thus emerge fromsurface 20 at different angles with respect to a surface normal.

It is noted that the spacing between channels 4 and the depth or aspectratio of individual channels 4 are not limited to be constant across thearea of sheet 2. According to one embodiment, at least one of the aboveparameters may be varied from one channel 4 to another. Additionally,the dihedral angle that channels 4 or one of its side walls form withrespect to surface 10 may also be varied within a predefined angularrange. According to one embodiment, it may be preferred that suchdihedral angle is equal or approximately equal to 90 degrees. In oneembodiment, it may be preferred that the dihedral angle varies within±10° from normal. In other words, the dihedral angle should preferablybe greater or equal to 80 degrees.

By way of example and not limitation, the above-described variations ofchannel 4 parameters may be used to control the bend angle for theredirected light rays or to provide a specific angular distribution oflight transmitted by sheet 2. Additionally, the perpendicular arrays ofchannels 4 may differ from each other in the way the channels are formedor arranged within the arrays.

FIG. 24 shows an exemplary configuration of the optical article of thepresent invention comprising sheet 2 and further comprising an externallight diffusing sheet 242. Diffusing sheet 242 is disposed parallel tosheet 2 and has a light diffusing texture in at least one of its majorsurfaces. In the non-limiting example illustrated in FIG. 24 , thesurface texture of sheet 242 is exemplified by a micro-lens array. Thelens array may be one-dimensional (lenticular lenses) ortwo-dimensional.

In operation, an off-axis parallel ray bundle 232 passes through sheet 2where at least some rays undergo TIR from reflective walls formed bychannels 4 and are deflected from the original propagation path into anew propagation direction which mirrors the propagation direction of theother rays with respect to normal 44. As a result of TIR andtransmission through sheet 2, the ray bundle 232 becomes split into twobeams and is distributed over a certain angular range. Upon exit fromsheet 2, rays of ray bundle 232 enter diffusing sheet 242 where therespective beams are further redistributed and diffused into a pluralityof divergent directions. Another exemplary off-axis parallel ray bundle234 first entering diffusing sheet 242 is dispersed before it furtherenters sheet 2. Sheet 2 further redistributes the rays so that theyobtain various propagation directions including those extending intoopposing hemispheres or quadrants with respect to normal 44 in the planeof reflection.

FIG. 25 explains operation of the optical article which is similar tothat of FIG. 24 except that diffusing sheet 242 is now disposed on theother side of sheet 2. In FIG. 26 , an illustrative example ofalternative configuration of the optical article is shown where sheet 2is sandwiched between two opposing diffuser sheets 242 and 244. Sucharrangement may be selected, for example, when a further improvement inlight diffusion is needed compared to the cases illustrated in FIG. 24and FIG. 25 .

FIG. 27 shows a non-limiting example of the optical article according toat least one embodiment, where surface 10 of sheet 2 has a lightdiffusing textured surface. The light diffusing texture is exemplifiedby a plurality of lenslets. Each lenslet represents an individualsurface relief feature 6 formed in surface 10.

In FIG. 28 , a variation of this embodiment is shown where similarlenslets are formed in surface 20 of sheet 2. In FIG. 29 , a yet furthervariation is shown in which surface relief features 6 are formed in bothsurfaces 10 and 20. It will be appreciated that the combination of TIRwalls of channels 4 and lenslets in either one or both of surfaces 10and 20 will provide an improved wide-angle redistribution and diffusionof at least off-axis rays compared to the diffusers employingrefractive-only features.

Example 1. FIG. 30 shows a photograph of a prototype sheet 2 made bycutting a grid of narrow channels 4 in a 0.25-inch acrylic (PMMA) sheetby means of material ablation using a 60-W CO₂ laser. The laser emits anarrow (about 6 mm) parallel beam with the wavelengths of about 10micrometers. The laser beam was made scanning across the surface ofsheet 2 using a Cartesian gantry system and a system of mirrors andfocused on the surface of the acrylic sheet using a 0.75″-diameter ZnSelens having a focal length of 2″. The laser beam scanning speed wasselected at about 14 mm/sec.

A first array of parallel channels was cut in one of the smooth surfacesof the acrylic sheet after which a second array of parallel channels wascut in a perpendicular direction in the same surface. The selectivematerial ablation by scanning the focused laser beam across the acrylicsheet surface has resulted in the formation of a rectangular grid ofnarrow and deep channels in the surface. The laser cutting process hascreated slightly tapered channels with heat-polished, curvilinear sidewalls extending transversally about % into the sheet thickness. Theintersecting perpendicular pairs of adjacent channels defined atwo-dimensional array of light-channeling cells each having four TIRwalls formed by the polished side walls of the channels.

A beam of parallel light was produced by a collimated LED light source.The finished laser-patterned sheet was illuminated by the collimatedlight source at incidence angles ranging from 0° to approximately 75°.The optical axis of the light source was tilted with respect to theplane of the acrylic sheet to create an off-axis angle of incidence. Theoff-axis direction of the incident beam was selected so that theprojection of said direction onto the sheet was parallel to thelongitudinal axis of one of the two intersecting arrays of the laser-cutchannels and perpendicular to the longitudinal axis of the other array.

In operation, the propagation of off-axis collimated light through theprototyped sheet 2 has resulted in splitting the beam into twowell-defined beams propagating generally towards the opposing ends ofthe acrylic sheet in the respective plane of reflection. The outputbeams were observed on a light scattering target disposed parallel tothe acrylic sheet. The target has revealed two distinct spots on theopposite sides from a normal to the plane of the sheet:

one corresponding to the beam portion that passed through the sheetwithout interacting with TIR walls and the other one corresponding tothe beam portion reflected from TIR walls. The angular distance betweenthe two spots was found to be approximately twice the incidence angle ofthe original off-axis parallel beam incident onto the acrylic sheet.

Likewise, when the off-axis tilt of the incident collimated beam wasazimuthally turned by 90 degrees with respect to the surface of theprototype sheet 2, thus causing the light beam interaction primarilywith the other (perpendicular) array of the laser-cut channels, theincident beam was split into two distinct beams in a perpendicularplane. Furthermore, exposing the laser-cut acrylic sheet to a collimatedbeam incident from a direction which projection onto the sheet surfacewas not parallel to either longitudinal axis has produced four distinctbeams demonstrating beam splitting in both perpendicular planes ofreflection.

Example 2. Laser-Cut Channels were Produced According to the Methoddescribed above in a ¼″ acrylic sheet having a light-scattering,matte-finish surface. The illumination of such light-scatteringvariation of sheet 2 with an off-axis beam with approximately 45°incidence angle has produced a broad, relatively evenly distributed,scattered beam of light spanning approximately ±60° from a normal tosheet 2 in the prevailing plane of beam propagation. The total angularspan of the scattered beam was around 120°. For comparison, the off-axisparallel beam illumination of a similar light-diffusing acrylic sheethaving no channels 4 and no TIR walls has resulted in much narrowerscattered beam (less than 60°) and light propagation only towards theopposing direction from the light source, exhibiting notably unequallight distribution on the target. Accordingly, the formation oflaser-cut TIR channels in the surface of acrylic sheet has produced alight beam which angular spread is approximately two times greater thanthat of the reference sheet. Additionally, the uniformity of thetransmitted light beam has been improved compared to the reference casedue to creating a nearly symmetric light distribution with respect to anormal to the sheet surface. Thus, when used in skylights orfenestration systems, such light-redirecting and light-spreading acrylicsheet may improve daylight penetration into under-illuminated parts ofthe building interior and also reduce glare associated with the directbeam of sunlight.

A second embodiment of the optical article of the present invention isdirected to a panel formed by a rectangular grid of specular reflectorsand used in conjunction with a broad-area light diffusing element. Suchan embodiment is illustrated in FIG. 31 showing a panel 22 whichincludes a specularly reflective grid 402 and light diffusing sheet 242disposed over the panel area of grid 402. Grid 402 has a form of aplanar panel and includes an open-cell grid formed by intersectingmirrored walls 408. Each mirrored wall 408 longitudinally extendsparallel to the prevailing plane of the panel and transversally extendsperpendicularly or nearly perpendicularly to such plane. Similarly tothe embodiment illustrated in FIG. 24 , light diffusing sheet 242 ofFIG. 30 may have lenslet-shaped surface relief features 6 or any othertype of light diffusing elements or surface texture.

In a non-limiting example, reflective grid 402 may be exemplified by theegg crate silver louver light panel manufactured by Plaskolite, Inc. Thelouver panel may be customarily made from acrylic of polystyrene withthe subsequent metallization for specular reflectivity.

In another non-limiting example, grid 402 may be exemplified by thesilver egg crate plastic lighting panel marketed by RidoutPlastics/Eplastics. The panel is commercially available in standard sizeof 2′×4′×0.5″ and has a specularly reflective metalized finish.

FIG. 32 illustrates an exemplary cross-section and operation of aportion of panel 22 shown in FIG. 31 . Referring to FIG. 32 ,horizontally disposed grid 402 includes a plurality of verticalreflective walls 408 which are made from an opaque rigid material andare also mirrored. Parallel horizontal planes 482 and 484 define theupper and lower boundaries of the panel 22. Sheet 242 disposed abovegrid 402 is designed to diffuse light incident from the above andtransmit it further to the reflective grid. Grid 402 further dispersesat least the off-axis rays by reflecting at least a portion of such raysfrom walls 408. The parameters of walls 408 and their spacing may beconfigured to provide for at least partial interception of the incidentoff-axis light and redistributing light into the opposing hemispheresrelatively to normal 44 to the panel. Likewise, walls 408 may bedesigned to provide any desired ratio between the amount of light thatpasses through grid 402 without striking any vertical wall and theamount of light that is redirected by one or more walls towards the sameor opposing edges of the panel in the plane of reflection.

FIG. 33 shows a different cross-sectional shape of reflective walls 408where each wall 408 is tapered towards the top and has reflectivesurfaces with curvilinear profiles. An advantage of using curvilinearprofiles for walls 408 can be that such configuration may provide agreater stiffness to grid 402 may. Additionally, a non-planar shape ofwalls 408 may further promote light flux dispersion and homogenization.

FIG. 34 shows an alternative mutual disposition of grid 402 and lightdiffusing sheet 242 in comparison to FIG. 33 . As it is shown, sheet 242may also be disposed below the grid 402 and configured to furtherdiffuse and redistribute light emerging from the grid panel.

In FIG. 35 , grid 402 is shown sandwiched between opposing paralleldiffusing sheets 242 and 244. In such configuration, the degree of lightdiffusion may be increased compared the case of a single light diffusingsheet although the total light transmission of panel 22 may be somewhatreduced compared to the same case.

FIG. 36 shows an exemplary implementation of the optical article withina skylight 502. The skylight can be ordinarily designed for rooftopinstallation and illumination of the building interior with the naturalsunlight used as a light source. According to one embodiment, the lightsource can also be an LED light source. According to one embodiment, theLED light source can be collimated and configured to produce a parallelbeam of light, e.g., as described in Examples 1 and 2.

Referring to FIG. 36 , skylight 502 includes a dome-shaped diffusersheet 260, optically transmissive sheet 2 and optional reflective sidewalls 512 and 514. Diffuser sheet 260 can be made from an opticallyclear plastic material, such as PMMA, polycarbonate and the like, andmay have at least one microstructured surface to improve lightdiffusion. Sheet 2 is also made from an optically transparent material,preferably PMMA, defined by opposing parallel surfaces 10 and 20. Sheet2 has at least one array of laser-cut deep and narrow channels 4extending vertically (along normal 44) between surface 10 towardssurface 20 and parallel to each other. Each channel 4 has opposing TIRwalls 8 and 26. Similarly to some of the embodiments illustrated inreference to FIG. 1 through FIG. 4 , channels 4 may also be arrangedinto two such arrays crossed at the right angle with respect to eachother thus forming a plurality of square or rectangular cells 30 eachdefined by four vertical TIR walls. Walls 512 and 514 of skylight 502are preferably covered with a sheet or film of specularly reflectivematerial to aid in channeling light from sheet 260 to sheet 2. Referringfurther to FIG. 36 , the optical article exemplified as skylight 502 canalso use one or more LEDs as a light source, according to at least someembodiments.

In operation, direct sunlight (or light emanated from an LED lightsource disposed above diffuser sheet 260) striking the diffuser sheet260 is dispersed across a limited angular range which will normallyinclude various off-axis rays that enter sheet 2. At least a portion ofsuch off-axis rays may pass through sheet 2 without interacting with anyof the walls 8 and 26 and thus emerge from surface 10 without a changein the propagation direction. At least a portion of rays may alsoreflect from one or more walls 8 and/or 26 and thus may change thepropagation direction resulting in a broad angular spread into theopposing quadrants relatively to normal 44 in the plane of reflection.Importantly, TIR walls 8 and/or 26 allow for a greater bend anglecompared to the transmissive diffusers employing surface microstructuresand may thus be configured to illuminate portions of the buildinginterior which would not otherwise be adequately illuminated.

In FIG. 37 , skylight 502 is shown to incorporate grid 402 whichreflective walls 408 redirect at least a portion of sunlight passingfrom the above through the grid. Accordingly, since the specularreflections within grid 402 result in effective bending of at leastoff-axis rays, the daylight distribution within the building can beimproved. This can be illustrated by the following reasoning. It will beappreciated that, in the absence of sheet 2 of FIG. 36 or reflectivegrid 402 of FIG. 37 , the sunlight entering skylight 502 from anoff-axis direction and shining through a conventional transmissivediffuser will tend to illuminate the room corner which is opposite tothe sun's direction. Since sheet 2 of FIG. 36 or reflective grid 402FIG. 37 can be configured to redistribute light between opposingdirections, the addition of the respective light redirecting componentsto the skylight may allow for illuminating the opposing corners of theroom without sacrificing the light transmission efficiency. Thus, as aminimum, skylight 502 can be configured to reduce the inherentover-illumination of some parts of the building interior andunder-illumination of the other parts of the building, the problemcommonly associated with conventional skylights. Moreover, therespective parts of skylight 502 may be configured to provide aboutequal illumination of the opposing parts of the building interior atleast for a predefined range of sun's elevations. According to oneembodiment, an LED light source can be disposed above diffuser sheet 260and configured to illuminate the optical article exemplified by skylight502 from the above. The LED light source can be further configured toilluminate diffuser sheet 260 from different angles, e.g., as depictedin FIG. 37 and/or discussed in Examples 1 and 2 above.

It is noted, in reference to FIG. 36 and FIG. 37 , that the type ofskylights in which the optical article can be incorporated is notlimited to the dome-shaped configurations, but can similarly be appliedto the case where the skylight can have any other suitable shape,including but not limited to a planar shape, pyramidal shape, prismaticshape, and the like. It is further noted that the front sheet of theskylight is not limited in type to those having light-diffusingmicrostructures. The present invention may also be applied to the caseof smooth-surface skylights which can be optically clear, translucent orpigmented and may have light transmissivity and/or light diffusionvarying in a broad range.

Further details of operation of the optical article exemplified by sheet2 or a combination of reflective grid 402 and one or more transmissivelight diffusers, as shown in the drawing figures, as well as itspossible variations will be apparent from the foregoing description ofpreferred embodiments. Although the description above contains manydetails, these should not be construed as limiting the scope of theinvention but as merely providing illustrations of some of the presentlypreferred embodiments of this invention. Therefore, it will beappreciated that the scope of the present invention fully encompassesother embodiments which may become obvious to those skilled in the art,and that the scope of the present invention is accordingly to be limitedby nothing other than the appended claims, in which reference to anelement in the singular is not intended to mean “one and only one”unless explicitly so stated, but rather “one or more.” All structural,chemical, and functional equivalents to the elements of theabove-described preferred embodiment that are known to those of ordinaryskill in the art are expressly incorporated herein by reference and areintended to be encompassed by the present claims. Moreover, it is notnecessary for a device or method to address each and every problemsought to be solved by the present invention, for it to be encompassedby the present claims. Furthermore, no element, component, or methodstep in the present disclosure is intended to be dedicated to the publicregardless of whether the element, component, or method step isexplicitly recited in the claims. No claim element herein is to beconstrued under the provisions of 35 U.S.C. 112, sixth paragraph, unlessthe element is expressly recited using the phrase “means for.”

What is claimed is:
 1. An optical article for illuminating buildinginteriors, comprising: a reflective grid panel comprising a plurality ofparallel longitudinal walls and a plurality of parallel transverse wallsjoining the plurality of parallel longitudinal walls and defining aplurality of rectangular openings configured to transmit light; an LEDlight source positioned above the reflective grid panel and configuredto illuminate the reflective grid panel at incidence angles ranging froma minimum angle of 0° to a maximum angle of at least 45°; a lightdiffusing sheet of an optically transmissive dielectric materialapproximately coextensive with and oriented generally parallel to thereflective grid panel; and a pair of reflective side walls flanking aspace between the reflective grid panel and the light diffusing sheet,wherein each of the parallel transverse walls extends transversely withrespect to a plane of the reflective grid panel and is configured todiffusely reflect a portion of light being transmitted through theplurality of rectangular openings.
 2. An optical article as recited inclaim 1, wherein the reflective grid panel is configured to be retainedin a horizontal orientation, wherein the parallel longitudinal walls andthe parallel transverse walls are formed from an opaque rigid material,and wherein the maximum angle is at least approximately 75°.
 3. Anoptical article as recited in claim 1, wherein the maximum angle is atleast approximately 75°, and wherein each of the plurality of parallellongitudinal walls extends transversely with respect to a plane of thereflective panel and is configured to diffusely reflect a portion of thelight being transmitted through the plurality of rectangular openings.4. An optical article as recited in claim 1, wherein the maximum angleis at least approximately 75°, and wherein the light diffusing sheet hasa curved shape.
 5. An optical article as recited in claim 1, furthercomprising a plurality of parallel channels formed in the lightdiffusing sheet, wherein the maximum angle is at least approximately75°.
 6. An optical article as recited in claim 1, further comprising aplurality of parallel channels formed in the light diffusing sheet andeach having at least one optically transmissive wall configured toreflect a portion of the light being transmitted through the pluralityof rectangular openings using a total internal reflection, wherein themaximum angle is at least approximately 75°.
 7. An optical article asrecited in claim 1, further comprising a plurality of parallel channelsformed in the light diffusing sheet, and further comprising a pluralityof lenticular lenses between the parallel channels, wherein the maximumangle is at least approximately 75°, and wherein at least one of theparallel channels has an optically transmissive wall configured toreflect light using a total internal reflection.
 8. An optical articleas recited in claim 1, further comprising a plurality of parallelchannels and a plurality of lenticular lenses formed in the lightdiffusing sheet, wherein the lenticular lenses are located in spacesbetween the parallel channels, wherein the maximum angle is at leastapproximately 75°, and wherein at least one of the parallel channels hasan optically transmissive wall configured to reflect light using a totalinternal reflection.
 9. An optical article as recited in claim 1,further comprising a plurality of parallel channels and a plurality oflenticular lenses formed in the light diffusing sheet, wherein thelenticular lenses are located in spaces between the parallel channels,wherein the maximum angle is at least approximately 75°, wherein atleast one of the parallel channels has an optically transmissive wallconfigured to reflect light using a total internal reflection, andwherein the optically transmissive wall forms an angle between 80degrees and 90 degrees with respect to the plane of the reflective gridpanel.
 10. An optical article as recited in claim 1, further comprisinga plurality of parallel channels formed in the light diffusing sheet,wherein at least one of the parallel channels has a pair ofsymmetrically disposed optically transmissive walls each configured toreflect light using a total internal reflection and forming an anglebetween 80 degrees and 90 degrees with respect to the plane of thereflective grid panel.
 11. An optical article as recited in claim 1,further comprising a plurality of parallel channels formed in the lightdiffusing sheet, wherein at least one of the parallel channels has apair of symmetrically disposed optically transmissive walls eachextending perpendicular to the plane of the reflective grid panel andconfigured to reflect light using a total internal reflection.
 12. Anoptical article as recited in claim 1, further comprising a plurality ofparallel channels and a plurality of lenticular lenses formed in thelight diffusing sheet, wherein the lenticular lenses are located inspaces between the parallel channels, wherein the maximum angle is atleast approximately 75°, wherein at least one of the parallel channelshas a pair of symmetrically disposed optically transmissive walls eachconfigured to reflect light using a total internal reflection andforming an angle between 80 degrees and 90 degrees with respect to theplane of the reflective grid panel.
 13. An optical article as recited inclaim 1, further comprising a plurality of parallel channels and aplurality of rounded ridges formed in the light diffusing sheet, whereinthe rounded ridges are located in spaces between the parallel channels,wherein the maximum angle is at least approximately 75°, wherein atleast one of the parallel channels has a pair of symmetrically disposedoptically transmissive walls each configured to reflect light using atotal internal reflection and forming an angle of less than 90 degreeswith respect to the plane of the reflective grid panel.
 14. An opticalarticle as recited in claim 1, further comprising a plurality ofparallel channels formed in the light diffusing sheet, wherein at leastone of the parallel channels has a pair of symmetrically disposedoptically transmissive walls each configured to reflect light using atotal internal reflection and forming an angle of less than 90 degreeswith respect to the plane of the reflective grid panel, and wherein eachspacing area located between adjacent channels comprises at least onelenticular lens.
 15. An optical article as recited in claim 1, wherein asurface of the light diffusing sheet comprises a plurality of lenticularlenses extending parallel to an edge of the light diffusing sheet, andwherein the maximum angle is at least approximately 75°.
 16. An opticalarticle as recited in claim 1, further comprising a plurality ofparallel channels and a plurality of lenticular lenses formed in thelight diffusing sheet, wherein the lenticular lenses are located inspaces between the parallel channels.
 17. An optical article as recitedin claim 1, further comprising a fluorescent optical element.
 18. Anoptical article as recited in claim 1, wherein the reflective grid panelis configured to be retained in a horizontal orientation, and wherein atleast one of the parallel transverse walls has a concave surface.
 19. Anoptical article for illuminating building interiors, comprising: areflective grid panel configured to be retained in a horizontalorientation and comprising a plurality of parallel longitudinal wallsformed from an opaque rigid material and a plurality of paralleltransverse walls joining the plurality of parallel longitudinal wallsand defining a plurality of rectangular openings configured to transmitlight; an LED light source positioned above the reflective grid paneland configured to illuminate the reflective grid panel at incidenceangles ranging from a minimum angle of 0° to a maximum angle of at least45° or more; a light diffusing sheet of an optically transmissivedielectric material disposed below the reflective grid panel, the lightdiffusing sheet being approximately coextensive with and orientedgenerally parallel to the reflective grid panel; and a pair ofreflective side walls flanking a space between the reflective grid paneland the light diffusing sheet, wherein each of the parallel transversewalls extends transversely with respect to a plane of the reflectivegrid panel and is configured to diffusely reflect a portion of lightbeing transmitted through the plurality of rectangular openings.
 20. Anoptical article as recited in claim 19, wherein the maximum angle is atleast approximately 75°.
 21. An optical article as recited in claim 19,wherein the light diffusing sheet has a curved shape.
 22. An opticalarticle as recited in claim 19, wherein the maximum angle is at leastapproximately 75°, and wherein the light diffusing sheet has a curvedshape.
 23. An optical article as recited in claim 19, wherein a surfaceof the light diffusing sheet comprises a plurality of lenticular lensesextending parallel to an edge of the light diffusing sheet.
 24. Anoptical article as recited in claim 19, further comprising a fluorescentoptical element.
 25. An optical article as recited in claim 19, whereinthe maximum angle is at least approximately 75°, and wherein at leastone of the parallel transverse walls has a concave surface.
 26. Anoptical article for illuminating building interiors, comprising: areflective grid panel configured to be retained in a horizontalorientation and comprising a plurality of parallel longitudinal wallsformed from an opaque rigid material and a plurality of paralleltransverse walls joining the plurality of parallel longitudinal wallsand defining a plurality of rectangular openings configured to transmitlight; an LED light source positioned above the reflective grid paneland configured to illuminate the reflective grid panel at incidenceangles ranging from a minimum angle of 0° to a maximum angle of at least45° or more; a light diffusing sheet of an optically transmissivedielectric material disposed above the reflective grid panel, the lightdiffusing sheet being approximately coextensive with and orientedgenerally parallel to the reflective grid panel; and a pair ofreflective side walls flanking a space between the reflective grid paneland the light diffusing sheet, wherein each of the parallel transversewalls extends transversely with respect to a plane of the reflectivegrid panel and is configured to diffusely reflect a portion of lightbeing transmitted through the plurality of rectangular openings.
 27. Anoptical article as recited in claim 26, wherein the maximum angle is atleast approximately 75°.
 28. An optical article as recited in claim 26,wherein the light diffusing sheet has a curved shape.
 29. An opticalarticle as recited in claim 26, wherein the maximum angle is at leastapproximately 75°, and wherein the light diffusing sheet has a curvedshape.
 30. An optical article as recited in claim 26, wherein a surfaceof the light diffusing sheet comprises a plurality of lenticular lensesextending parallel to an edge of the light diffusing sheet.
 31. Anoptical article as recited in claim 26, further comprising a fluorescentoptical element.
 32. An optical article as recited in claim 26, whereinthe maximum angle is at least approximately 75°, and wherein at leastone of the parallel transverse walls has a concave surface.